1. Field of the Invention
The present invention relates to an improved method for production of phenol and acetone by decomposition of cumene hydroperoxide to phenol, acetone, and .alpha.-methylstyrene in the presence of an acidic catalyst. The improvement comprises neutralization of the acidic catalyst after substantial completion of the decomposition by addition of a substituted amine.
2. Related Background Art
One of the predominant commercial processes for manufacture of phenol is the cumene oxidation process, in which cumene is oxidized in air to produce cumene hydroperoxide (CHP). The CHP is then cleaved to phenol and acetone in the presence of an acidic catalyst. This process also produces .alpha.-methylstyrene (AMS), along with other byproducts, including acetophenone, dimethylphenylcarbinol, and cumylphenols. Typically, the acidic catalyst is a strong, and not heavily corrosive inorganic acid, such as sulfuric or phosphoric acid. The acidic catalyst must be removed or neutralized to prevent further, unwanted reactions in the downstream purification steps that produce the phenol and acetone products.
Typically, commercial processes for manufacture of phenol from CHP use inorganic bases, ion exchange resins, or a combination thereof to remove acidity from the crude product stream. Since ion exchange resins are temperature sensitive, the crude product stream must be cooled substantially prior to contact with the resin. The need to cool the product stream increases energy costs significantly because the crude product stream must then be re-heated prior to downstream purification operations. A further drawback of ion exchange resins is that they must be regenerated frequently, a labor-intensive and costly process which also results in formation of large amounts of aqueous waste. Moreover, ion exchange resins give a highly variable final pH in the crude product stream, adversely affecting final product yields, and can also release alkali salts which cause fouling of equipment.
The use of a strong base, such as sodium hydroxide or potassium hydroxide to neutralize the acidic catalyst is not desirable because it is difficult to achieve accurate pH control in a neutralization reaction between a strong acid and a strong base. Moreover, metal hydroxides generate salts that have a propensity to deposit on heat exchange surfaces, causing fouling and decreasing efficiency.
The use of ammonia to neutralize the acidic catalyst is disclosed in U.S. Pat. No. 5,254,751 to Zakoshansky. In the process described in this reference, neutralization with ammonia is performed during the CHP decomposition, rather than after the decomposition. The disclosure states that the ammonium salts produced from addition of ammonia to the reaction mixture act as acidic catalysts for the remainder of the CHP decomposition reaction. This reference suggests that hydrazine and alkylamines having one to five carbon atoms are suitable for neutralization during CHP decomposition, but that ammonia is preferred, especially for neutralizing sulfuric acid. Zakoshansky also suggests a maximum operating temperature of 110.degree. C.